Use of Enhanced CO2 Removal Solvents

The CO2 formed in the gasification process and the shift conversion process is generally removed by scrubbing with a solvent. Conventional CO2 removal applies a chemical absorption method using an absorbing liquid. The solvents used in chemical absorption processes are mainly aqueous amine solutions, such as monoethanolamine (MEA), or hot potassium carbonate solutions. The capture of CO2 with solvents requires mechanical energy to circulate the solvent and heat to regenerate the solution. An almost pure CO2 stream is recovered (1.3-1.4 t CO2/t NH3), which is typically vented or can be used in other (industrial) processes, such as urea production (UNEP, 1998 p.12). The energy consumption of the CO2 removal system depends on the solvent used, the way the system is incorporated in the ammonia plant, and is affected by syngas purity and CO2 recovery.

The solvent monoethanolamine (MEA) has been widely used in the ammonia production process, but has some significant drawbacks including the considerable amount of energy required for regeneration. Improved solvents, which require less energy for regeneration of the solution, include the Benfield process (HiPure and LoHeat) and BASF’s two-stage activated diethanolamine (aMDEA) (EFMA, 2000 p.13; UNEP, 1998 p.12). 

A potential additional advantage is that the reduction in energy consumption, by using improved solvents in the CO2 capture process, may allow a reduction in the steam-carbon ratio in the primary reforming section. Lower reboiler duty also allows for an increase in the plant capacity without any modification of equipment (CEAMAG, 2009). 

Conventional CO2 removal applies a chemical absorption method, however, CO2 can also be removed using physical absorption. Physical absorption processes use an organic solvent, which absorbs CO2 as a function of the partial pressure. The high CO2 loadings result in low circulation rates and less utility costs for these type of processes (Kunjunny et al., unknown date). Physical absorption solvents typically used in ammonia production processes include glycol dimethylethers (Selexol) and propylene carbonate (IPTS/EC, 2007 p.41; EFMA, 2000 p.13). Regeneration of the solution is performed by vacuum flashing and air stripping and consumes significantly less energy than in chemical absorption.

improved solvents for CO2 removal can be applied to all new and existing ammonia plants. The type of removal process depends on the lay-out of the ammonia plant and on the requirements posed on the CO2, e.g. purity (IPTS/EC, 2007 p.75; de Beer et al., 2001 p.22).   

Development Status Products

Use of Enhanced CO2 Removal SolventsCosts & Benefits

Parent Process: Gas Refining
Energy Savings Potential
CO2 Emission Reduction Potential

Investment costs of improved solvents are estimated at €15 per GJ saved annually (de Beer et al., 2001.,  p.22).

The investment for the use of improved solvents for CO2 recovery are estimated to be around €3/GJ (Nieuwlaar, 2001. p.22).

Japanese flag For a 300 000 tonne/y plant, the investment costs for switching over to Selexol are reported to be around 1 200 millon Yen, providing yearly savings of 470 million Yen and resulting in a payback time or  2.5 years (ECCJ, 1999. p. 160).

Indian flag The cost of revamping from MEA to aMDEA in the Indian plant totaled  US $ 1.25 million (Vaish and Patel, 2002).

Use of Enhanced CO2 Removal Solvents Publications

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Directory of Energy Conservation Technology in Japan - Section 3: Chemical Industry

Prepared by New Energy and Industrial Technology Development Organization and the Energy Conservation Center, Japan, this extensive directory covers an extensive list of energy saving measures applicable to diverse range of industries. Section 3 concentrates on measures applicable to chemical industry, including ammonia production.

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ICARUS-4 - Sector Study for the Chemical Industry

This report by Evert Nieuwlaar provides information on energy consumption in 1995 and the energy consumption potential that exists within the chemical industry in the Netherlands. The data is intended for inclusion in ICARUS - 4 database, which gives an inventory of technical options for energy savings in all sectors in Netherlands. 

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Use of Enhanced CO2 Removal Solvents Reference Documents

Reference Document on Best Available Techniques for the Manufacture of Large Volume Inorganic Chemicals - Ammonia, Acids and Fertilisers

Prepared by the Institute for Prospective Technical Studies of European Commision, this document provides detalied information on Best Available Technologies applicable to Ammonia production – as well as on the production of Acids and Fertilizers.  

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41, 75-76

Use of Enhanced CO2 Removal Solvents Guidelines

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Use of Enhanced CO2 Removal Solvents Websites